Advances in technology have led to improvements in the precision of guided munitions. However, as guidance systems have become more sophisticated, the need for even greater precision is apparent. As military targets are frequently found in civilian surroundings, highly precise guidance systems are required to destroy these military targets while minimizing collateral damage to the civilian surroundings. One approach to increasing the precision of guided munitions is through using a laser designator to illuminate the desired target. A quadrant detector within the radome of the guided munition then guides the munition to maximize the reflected laser signal received from the illuminated target.
While such laser guided munitions have been in operation for quite some time, the radome/detector design limits the velocity of these guided munitions. In particular, many of the radome/detector designs include a hemispherical radome. The velocity of a guided munition having a hemispherical radome is limited due to the radome's aerodynamic drag. In an effort to reduce this aerodynamic drag, the use of more conic-shaped radomes has been attempted. However, this change in radome shape has created problems for the detector system used to guide the munition. Moreover, the simple quadrant detectors used in a hemispherical radome are incompatible with the optical transmission properties of a more conic-shaped radome.
Further, while laser guided munitions exist, the requirement of using a continuous laser for illuminating the target is undesirable. The use of a continuous laser creates a beacon for anti-aircraft batteries wishing to destroy the aircraft guiding the munition. For this reason, the use of a pulsed laser is desirable. This creates additional guidance problems as the guided munition receives far less reflected laser signal, resulting in the need for more accurate guidance feedback based upon this limited reflected laser signal. This requirement for accuracy in spite of limited reflected laser signal is even greater when the velocity of the guided munition increases.
One alternative to the use of hemispherical, optical radiation based guidance systems is the use of radio frequency based guidance systems. Quadrant detectors based upon receiving radio frequency radiation permit more conic-shaped radomes. However, they require a local oscillator for coherent detection. For this reason, optical radiation based systems that do not employ coherent detection are desirable due to their reduced complexity.
Thus, a new approach for detecting an optical radiation signal that allows for greater guided munition velocities is needed that provides greater sensitivity for more accurate guidance of the munition. Moreover, a new approach is needed that is compatible with a conic-shaped radome.